Reflexes are not always good predictors of clinical pain. There is a need for methods for measuring pain responses of animals at the conscious level. The Aim of this Project is to develop an apparatus for testing operant nociceptive responses "conscious pain sensitivity" exhibited by rodents. This apparatus can be used to evaluate the effect of a disease state, drug, surgical procedure or other intervention, on pain sensitivity. The apparatus will be designed to measure a conscious escape response to painful hot and cold stimuli and an aversive non-painful bright light stimulus. The apparatus will include two chambers connected by a portal which will allow the test animal to pass between the two chambers even if the animal is tethered to infusion cannulas, cables, or other diagnostic or delivery devices. The two chambers will be able to independently produce painful conditions by using floors that can be rapidly heated or rapidly cooled using Peltier devices. Therefore the floor of each chamber can be at a comfortable temperature, or painfully hot or painfully cold (two way shuttle test). The ability to change floor temperature rapidly allows for repeated trials with minimal avoidance learning. Each chamber will be able to produce an aversive, non-painful condition, using bright light. The bright light in each chamber can be independently turned on or off (two way control). The two chambers will be equipped with photo-electronic sensing devices to automatically record the movements of the animal between the two chambers. Computer software will control the experimental conditions and record escape latency measurements, place preference data, and baseline control data. The apparatus can be outfitted with a tether to the rodent to allow the application of electrical or chemical stimuli or to take biological samples. Stimulation through the tether can be in lieu of, or concurrent with, the thermal floor stimuli. Thus the apparatus will be flexible and applicable to a variety of pain sensitivity studies.